This invention is in the general field of methods of preparing saccharide fragments.
Saccharides are important as commodity chemicals and are used often in food and industrial applications. They are also important specialty chemicals in biotechnology, e.g., in the preparation of antibiotics or antibodies, as antigens for vaccines, or as diagnostic reagents.
Saccharides may be obtained from natural sources or synthesized enzymatically or chemically. Synthesis of saccharides having more than about five monosaccharide units often is difficult, especially if one of the units is sialic acid, which is acid labile. Enzymatic synthesis is limited by the available enzymes and substrates and may be relatively expensive.
While natural polysaccharides are sometimes available, in some situations, their use presents problems when they are too large. For example, many food and industrial applications require polysaccharides of specific sizes, and some native polysaccharides may be far too large. In some applications, decreasing the size of the polysaccharide can improve ease of handling and lower production costs. Where a cross-linked saccharide is desired, e.g., to enhance immunogenicity when used in a vaccine, available materials of high molecular weight may form insoluble gels when cross-linked. Reducing the chain length of the starting saccharide can avoid this problem.
Polysaccharides can be cleaved into smaller molecular weight fragments by acid, base, or enzymatic-catalyzed hydrolysis. Acid catalyzed degradation may cleave polysaccharides nonselectively in both carbohydrate and other functional moieties, yielding inconsistent products or non-functional products. For example, sialic acids are found on the carbohydrate moieties of many biologically important polysaccharides and can be determinants of biological functions, including recognition and attachment. They can also be determinants of epitopes for antibody generation and as such should be conserved in attempts to generate saccharide fragments, from polysaccharides. Sialic acids, however, are readily removed by acid.
Enzymatic hydrolysis of polysaccharides can be highly specific but it is usually limited to applications where an enzyme with the desired specificity is readily available. Some saccharide fragments may alternatively be isolated directly from natural sources, but these naturally occurring shorter polysaccharides typically exist in limited quantity. In some cases, saccharide fragments may be chemically and/or enzymatically synthesized. However, even in those cases the enzymes and substrates necessary to conduct the synthesis may be expensive. In general, the synthesis of saccharide fragments of more than five monosaccharide residues can be extremely difficult.